Singulation (i.e. separation) of dies (chips) fabricated on a semiconductor wafer is conventionally performed by mechanical dicing (sawing), dry laser dicing, water-jet guided laser dicing, stealth dicing via pulsed laser or plasma dicing. In the case of thin dies with a thick backside metal layer needed for mechanical stabilization, the structuring of the backside metal stack composed of a variety of different metal layers such as Cu on the wafer is necessary prior to the separation of the semiconductor dies in order to avoid chipping and metal burr formation. This structuring of the thick backside metallization is typically done by pattern plating or wet etching, which are both limited to thin metal stabilization layers of approximately 20 μm to 40 μm thick. Wet chemical structuring of thick backside metal stacks with thicknesses of approximately 40 μm to 100 μm and larger is very expensive and results in lateral etching and hence non-perpendicular metal sidewalls. In the case of mechanical dicing, the sidewalls of the dies can be damaged with cracks which propagate during the sawing process.
In the case of laser-based dicing, the penetration depth of the laser radiation into the bulk semiconductor causes excessive heating of the underlying semiconductor dies. This excessive heating leads to chemical formation of metal-semiconductor compounds such as Cu-silicide on the sidewalls of the dies. The metal-semiconductor compound diffuses into the semiconductor bulk and degrades the electrical performance of the dies to be separated. The excessive heating resulting from laser-based dicing also causes localized melting of the backside metallization.